Fats and Oils
Fats and oils are a broad class of animal and vegetable compounds which are used in products such as foods, cleansers, and lubricants. They are members of the lipid family and are energy-rich compounds that are basic components of the normal diet. Fats and oils have essentially the same chemical structure--a mixture of fatty acids combined with glycerol (a trihydroxy alcohol) and are similarly insoluble in water. However, while fats remain solid (or semisolid) at room temperature, most oils very quickly become liquid at increased temperatures. Unfortunately, this definition can lead to confusion with petroleum and essential oils. Therefore chemists have begun to classify both as fats. Animal fats and oils include butter, lard, tallow and fish oil. Plants provide a number of oils, such as cottonseed, peanut and corn oils.
The fundamental nature of natural fats and oils was determined almost two hundred years ago by the French chemist Michel Eugéne Chevreul. Back in 1811--when Chevreul first began his investigation of animal fats--the science of organic chemistry was still in its earliest stages. Chevreul began simply enough by analyzing a potassium soap that had been made from pig fat. After treating the soap with various chemicals, he found that it yielded a crystalline material with acid properties--the first fatty acid to be discovered.
During the next decade, Chevreul decomposed a variety of soaps, most of which had been made from different animal fats. Not surprisingly, he obtained a whole series of fatty acids from these soaps. After isolating and studying the fatty acids, he gave them names--such as butyric acid and stearic acid which are still used today. By 1816 he also established the fact that animal fats were composed not only of fatty acids, but also of glycerol, an alcohol that, in 1783, another chemist, Carl Scheele, had already found in both olive oil and in other vegetable and animal fats.
Since Chevreul's time, a great deal more has been discovered about the chemical structure of fats. For one thing, chemists have found that, in food, fats are primarily triglycerides, which are composed of one molecule of glycerol and three molecules of fatty acids. And, while the glycerol component tends to remain the same in virtually all fats, the fatty acids themselves come in a variety of types and configurations.
The typical fatty acid is simply a chain of carbon atoms with hydrogen atoms attached to them. The length of the chain can vary widely, however, most range from four carbon atoms to 24 or more. Most edible fats and oils have 16 to 18 carbon atoms and are considered long-chained. The degree of saturation can also vary, depending on the number of hydrogen atoms in the chain. The chain with the maximum number of hydrogen atoms, for instance, is considered saturated. Saturated fats usually come from animal sources, have very high melting points, and--most importantly--can often increase the body's blood cholesterol and, by so doing, possibly contribute to the onset of certain diseases such as atherosclerosis.
Most of the nutritionally important fatty acids can be synthesized by the body from other substances but a few must be supplied by the diet. These are the ones termed essential fatty acids (EFAs). Among EFAs, linoleic acid is considered the most valuable. The most abundant polyunsaturated fatty acid in nature, linoleic acid helps maintain the function of cellular and subcellular membranes and is involved in the synthesis of prostaglandins, which are potent substances that appear to mimic or inhibit many hormones. A deficiency of this essential fatty acid, seen most often in poorly-nourished infants and young children, causes dry, scaly skin and some delay in wound healing.
Fats have two main functions: they provide some of the raw material for synthesizing and repairing tissues and they serve as a concentrated source of fuel energy. Fats, in fact, provide humans with roughly twice the energy, per unit weight, as do carbohydrates and proteins --nine kilocalories per gram (Kcal/gram) versus about four Kcal/gram for either sucrose or most proteins. Fats are not only an important source of day-to-day energy, they can, if not immediately needed, be stored indefinitely as adipose tissue in case of future need.
Fats also help transport fat-soluble vitamins throughout the system; cushion and form protective pads around delicate organs, such as the heart, liver and kidneys; make up the layer of fat under the skin that helps insulate the body against too much heat loss; and even add to the palatability of other foods that might otherwise be inedible.
While normal amounts of fat in the diet are essential to good health, unnecessarily high amounts can lead to a number of problems. For instance, a certain amount of excess adipose tissue can be valuable during periods of illness, overactivity, or food shortages; however, too much adipose tissue can not only be unsightly but can overwork the heart and put added stress on other parts of the body. High levels of certain circulating fats may not only lead to atherosclerosis, but have been linked to other illnesses, including cancer.
How much fat in the diet is considered too much? In the past, nutritionists considered reasonable a diet that obtained 40 percent of its calories from fats. These days, however, they recommend that no more than 30 percent (and preferably even less) come from fat. In healthy adults, too, body fats typically should make up no more than 18-25 percent body weight in females and 15-20 percent in males.
New research on fats and oils has continued into the 1990s. For example, a 1997 report details attempts by genetic engineers to develop enzymes which will allow plants to convert saturated fats and oils to healthier unsaturated materials. In addition to nutritional applications, advances have been made on oils for other applications. Because they are environmentally friendly, renewable resources, an increasing number of plant oils are being evaluated for use as industrial lubricants. Two examples which are anticipated to have a significant industrial impact are the well known soybean oil and the lesser known meadowfoam oil.
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